Perhaps by no coincidence, Pinellas County deputies also found a similar device earlier this week at a Circle K Shell station at 13098 Walsingham Road in Largo.

"This could be the tip of the iceberg at this point. We just really don't know how many are out there," said Sgt. Mike Puetz with the St. Petersburg police.

"We know about the two cases right now, but that would suggest to us there are more out there we just don't know about.," Puetz said.

Police say if you see wires sticking out of a card slot, or if it appears loose or damaged, don't use it. Also, if you see tape or tape residue -- or if the card reader looks out of place, perhaps off-color from the rest of the machine -- alert the gas station clerk right away.

"And it seems like we'll have situations where these will go a way for a period of time and then they'll come back," Puetz said.

Shell issued a skimmer warning in five Florida cities in May of this year, including Sarasota.

It's also good advice, say investigators, to check your financial accounts regularly and contact your bank or credit card company immediately if there has been any suspicious activity.

Police say there's clear evidence this has been going on for awhile in St. Petersburg.

Law enforcement also got a call Tuesday from a man who had purchased gas at the Shell station on Roosevelt Boulevard on June 20. Four days later, he told them, he spotted an unauthorized $1,000 charge on his account.